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Apache Spark 2.4.0 正式发布

Apache Spark 2.4 与昨天正式发布,Apache Spark 2.4 版本是 2.x 系列的第五个版本。

即将发布的 Apache Spark 2.4 都有哪些新功能
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Apache Spark 2.4 为我们带来了众多的主要功能和增强功能,主要如下:

  • 新的调度模型(Barrier Scheduling),使用户能够将分布式深度学习训练恰当地嵌入到 Spark 的 stage 中,以简化分布式训练工作流程。
  • 添加了35个高阶函数,用于在 Spark SQL 中操作数组/map。
  • 新增一个新的基于 Databricks 的 spark-avro 模块的原生 AVRO 数据源。
  • PySpark 还为教学和可调试性的所有操作引入了热切的评估模式(eager evaluation mode)。
  • Spark on K8S 支持 PySpark 和 R ,支持客户端模式(client-mode)。
  • Structured Streaming 的各种增强功能。 例如,连续处理(continuous processing)中的有状态操作符。
  • 内置数据源的各种性能改进。 例如,Parquet 嵌套模式修剪(schema pruning)。
  • 支持 Scala 2.12。

具体的介绍可以参见《即将发布的 Apache Spark 2.4 都有哪些新功能》 文章的介绍。以下是各个模块解决的 ISSUE 列表。

Core and Spark SQL

  • 主要功能
    • Barrier Execution Mode: [SPARK-24374] 调度器中支持 Barrier Execution Mode,使得 Spark 可以更好地和 机器学习框架进行整合;
    • Scala 2.12 Support: [SPARK-14220] 添加对 Scala 2.12 的支持。 现在,您可以使用 Scala 2.12 构建 Spark ,并使用 Scala 2.12 中编写 Spark 应用程序。
    • Higher-order functions: [SPARK-23899] 添加许多新的内置函数,包括高阶函数,可以更轻松地处理复杂数据类型。
    • Built-in Avro data source: [SPARK-24768] Inline Spark-Avro package with logical type support, better performance and usability.
  • API
  • Performance and stability
    • [SPARK-16406] Reference resolution for large number of columns should be faster
    • [SPARK-23486] Cache the function name from the external catalog for lookupFunctions
    • [SPARK-23803] Support Bucket Pruning
    • [SPARK-24802] Optimization Rule Exclusion
    • [SPARK-4502] Nested schema pruning for Parquet tables
    • [SPARK-24296] Support replicating blocks larger than 2 GB
    • [SPARK-24307] Support sending messages over 2GB from memory
    • [SPARK-23243] Shuffle+Repartition on an RDD could lead to incorrect answers
    • [SPARK-25181] Limited the size of BlockManager master and slave thread pools, lowering memory overhead when networking is slow
  • Connectors
    • [SPARK-23972] Update Parquet from 1.8.2 to 1.10.0
    • [SPARK-25419] Parquet predicate pushdown improvement
    • [SPARK-23456] Native ORC reader is on by default
    • [SPARK-22279] Use native ORC reader to read Hive serde tables by default
    • [SPARK-21783] Turn on ORC filter push-down by default
    • [SPARK-24959] Speed up count() for JSON and CSV
    • [SPARK-24244] Parsing only required columns to the CSV parser
    • [SPARK-23786] CSV schema validation - column names are not checked
    • [SPARK-24423] Option query for specifying the query to read from JDBC
    • [SPARK-22814] Support Date/Timestamp in JDBC partition column
    • [SPARK-24771] Update Avro from 1.7.7 to 1.8
  • Kubernetes Scheduler Backend
  • PySpark
    • [SPARK-24215] Implement eager evaluation for DataFrame APIs
    • [SPARK-22274] User-defined aggregation functions with Pandas UDF
    • [SPARK-22239] User-defined window functions with Pandas UDF
    • [SPARK-24396] Add Structured Streaming ForeachWriter for Python
    • [SPARK-23874] Upgrade Apache Arrow to 0.10.0
    • [SPARK-25004] Add spark.executor.pyspark.memory limit
    • [SPARK-23030] Use Arrow stream format for creating from and collecting Pandas DataFrames
    • [SPARK-24624] Support mixture of Python UDF and Scalar Pandas UDF
  • Other notable changes
    • [SPARK-24596] Non-cascading Cache Invalidation
    • [SPARK-23880] Do not trigger any job for caching data
    • [SPARK-23510] Support Hive 2.2 and Hive 2.3 metastore
    • [SPARK-23711] Add fallback generator for UnsafeProjection
    • [SPARK-24626] Parallelize location size calculation in Analyze Table command

Programming guides: Spark RDD Programming Guide and Spark SQL, DataFrames and Datasets Guide.

Structured Streaming

  • Major features
    • [SPARK-24565] Exposed the output rows of each microbatch as a DataFrame using foreachBatch (Python, Scala, and Java)
    • [SPARK-24396] Added Python API for foreach and ForeachWriter
    • [SPARK-25005] Support “kafka.isolation.level” to read only committed records from Kafka topics that are written using a transactional producer.
  • Other notable changes
    • [SPARK-24662] Support the LIMIT operator for streams in Append or Complete mode
    • [SPARK-24763] Remove redundant key data from value in streaming aggregation
    • [SPARK-24156] Faster generation of output results and/or state cleanup with stateful operations (mapGroupsWithState, stream-stream join, streaming aggregation, streaming dropDuplicates) when there is no data in the input stream.
    • [SPARK-24730] Support for choosing either the min or max watermark when there are multiple input streams in a query
    • [SPARK-25399] Fixed a bug where reusing execution threads from continuous processing for microbatch streaming can result in a correctness issue
    • [SPARK-18057] Upgraded Kafka client version from 0.10.0.1 to 2.0.0

Programming guide: Structured Streaming Programming Guide.

MLlib

  • Major features
  • Other notable changes
    • [SPARK-22119] Add cosine distance measure to KMeans/BisectingKMeans/Clustering evaluator
    • [SPARK-10697] Lift Calculation in Association Rule mining
    • [SPARK-14682] Provide evaluateEachIteration method or equivalent for spark.ml GBTs
    • [SPARK-7132] Add fit with validation set to spark.ml GBT
    • [SPARK-15784] Add Power Iteration Clustering to spark.ml
    • [SPARK-15064] Locale support in StopWordsRemover
    • [SPARK-21741] Python API for DataFrame-based multivariate summarizer
    • [SPARK-21898] Feature parity for KolmogorovSmirnovTest in MLlib
    • [SPARK-10884] Support prediction on single instance for regression and classification related models
    • [SPARK-23783] Add new generic export trait for ML pipelines
    • [SPARK-11239] PMML export for ML linear regression

Programming guide: Machine Learning Library (MLlib) Guide.

SparkR

  • Major features
    • [SPARK-25393] Adding new function from_csv()
    • [SPARK-21291] add R partitionBy API in DataFrame
    • [SPARK-25007] Add array_intersect/array_except/array_union/shuffle to SparkR
    • [SPARK-25234] avoid integer overflow in parallelize
    • [SPARK-25117] Add EXCEPT ALL and INTERSECT ALL support in R
    • [SPARK-24537] Add array_remove / array_zip / map_from_arrays / array_distinct
    • [SPARK-24187] Add array_join function to SparkR
    • [SPARK-24331] Adding arrays_overlap, array_repeat, map_entries to SparkR
    • [SPARK-24198] Adding slice function to SparkR
    • [SPARK-24197] Adding array_sort function to SparkR
    • [SPARK-24185] add flatten function to SparkR
    • [SPARK-24069] Add array_min / array_max functions
    • [SPARK-24054] Add array_position function / element_at functions
    • [SPARK-23770] Add repartitionByRange API in SparkR

Programming guide: SparkR (R on Spark).

GraphX

  • Major features
    • [SPARK-25268] run Parallel Personalized PageRank throws serialization Exception

Programming guide: GraphX Programming Guide.

Deprecations

Changes of behavior

  • Spark Core
  • Spark SQL
    • [SPARK-23549] Cast to timestamp when comparing timestamp with date
    • [SPARK-24324] Pandas Grouped Map UDF should assign result columns by name
    • [SPARK-23425] load data for hdfs file path with wildcard usage is not working properly
    • [SPARK-23173] from_json can produce nulls for fields which are marked as non-nullable
    • [SPARK-24966] Implement precedence rules for set operations
    • [SPARK-25708] HAVING without GROUP BY should be global aggregate
    • [SPARK-24341] Correctly handle multi-value IN subquery
    • [SPARK-19724] Create a managed table with an existed default location should throw an exception

Please read the Migration Guide for all the behavior changes

Known Issues

  • [SPARK-25271] CTAS with Hive parquet tables should leverage native parquet source
  • [SPARK-24935] Problem with Executing Hive UDAF’s from Spark 2.2 Onwards
  • [SPARK-25879] Schema pruning fails when a nested field and top level field are selected
  • [SPARK-25906] spark-shell cannot handle -i option correctly
  • [SPARK-25921] Python worker reuse causes Barrier tasks to run without BarrierTaskContext
  • [SPARK-25918] LOAD DATA LOCAL INPATH should handle a relative path
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